Method and device for cold-forming rolling elements

ABSTRACT

A method for cold-forming rolling elements in the form of bodies of revolution with external rolling surfaces having straight or curved generatrices extending between portion of relatively large and relatively small diameter uses a generally cylindrical blank. The diameter of the blank is substantially equal to the greatest diameter of the element to be formed. The blank is forced into a die cup having an internal profile which is identical to the rolling surface profile, against a counter-force which increases as the blank is forced into the cup. The penetration of the blank into the cup is halted at a predetermined stage. The invention is applicable to forming bearing rollers.

United States Patent Orain Aug. 19, 1975 METHOD AND DEVICE FOR 2,267,22912/1941 Zimmerman 29 149.5 R

COLD FORMING ROLLING ELENIENTS 3,513,683 5/1970 Moore 72/359 75Inventor: Michel Grain, FOREIGN PATENTS OR APPLICATIONSConflans-Sainte-Honoflne, France 56,819 5/1891 Germany 72/354 [73]Assignee: lS)oc iete tFXnOnyme: Glaenzer Spicer, Primary ExaminerRichard J. Herbst olssy rmce Attorney, Agent, or FirmBaldwin, Wight &Brown [22] Filed: June 29, 1973 Appl. No.: 375,122

Foreign Application Priority Data July 10, 1972 France 72.24973References Cited UNITED STATES PATENTS 10/1920 Rydbeck 72/354 1/1934Langhammer 29/149.5 R

[ 5 7 ABSTRACT is halted at a predetermined stage. The invention isapplicable to forming bearing rollers.

6 Claims, 7 Drawing Figures PATENTED A1161 9 I915 sum 2 05 1 METHOD ANDDEVICE FOR COLD-FORMING ROLLING ELEMENTS The present invention concernsthe cold-forming of rolling elements such as rollers for homokineticcouplings or bearings having a tapering rolling surface which may beconical, part-spherical or toroidal for example.

In the conventional process steel rollers are formed by machining ablank on a lathe, quenching the machined blank and finishing the rollingsurfaces, the end faces and the bore. These machining and finishingoperations, which are essential for maintaining precision and constantdimensions, must be carried out in 'sequence on special machines, whichresult in high costs.

The object of the invention is a method with which rollers of constanthigh-precision dimensions can be very economically produced from blanksrequiring only very simple preparatory machining, using a single machinerequiring only a single working stroke.

In accordance with the invention there is provided a method forcold-forming a rolling element comprising a body of revolution with anexternal rolling surface having straight or curved generatricesextending between a portion of relatively large diameter and a portionof relatively small diameter, in which method a cylindrical blank, thediameter of which is substantially equal to the maximum diameter of theelement, is compressed in a cup whose internal profile is identical tothe external profile of the element by overcoming an increasingcounter-pressure exerted on the blank, the forcing of the blank into thecup being halted at a predetermined stage.

The invention also includes apparatus for carrying out this method, theapparatus comprising a die formed with a cup having an internal wall theprofile of which is identical to the external profile of the rollingsurface of the element and which communicates via a conical extension ofthe wall with a plane bearing face of the die which is perpendicular tothe axis of revolution of the cup, the die being formed with a passageextending the cup surface remote from the plane bearing face and havinga diameter substantially equal to the smallest diameter of the element,a sliding ejector being disposed in the bore and engaging resilientmeans arranged to provide a force resisting movement of the ejector intothe passage and which increases with the degree of penetration, theapparatus further comprising a plunger having a first bearing faceadapted to engage the bearing face of the die and a circular secondbearing face projecting from the first bearing face, having the sameform as the greatest diameter face of the element, and being arranged toenter the conical extension of the cup wall, the die and plunger beingmounted for relative displacement so that the second bearing face of theplunger enters the cup, while being maintained strictly coaxial with thecup, until the first bearing face of the plunger engages the bearingface of the die.

When the rolling element comprises an axial bore the blank is formedwith a corresponding bore, preferably of slightly greater diameter thanthat of the finished element, and a mandrel provided with externalbumishing elements and projecting into the die cup through the hollowejector is mounted for coaxial movement within the ejector, the mandreland bumishing elements having a diameter identical to that of the borein the element.

Examples of applications of the invention are described in detailhereinafter with reference to the accompanying drawings in which:

FIG. 1 is a diametral section of a half-roller with a part-sphericalexternal surface cold-formed in accordance with the invention;

FIG. 2 is an analogous view of the blank from which the half-roller ofFIG. 1 is formed;

FIG. 3 is an axial vertical section of a machine for forming thehalf-roller of FIG. 1 from the blank of FIG. 2, shown in an initialoperative position;

FIG. 4 is an analogous section of the machine in its final workingposition;

FIG. 5 is a side elevation of a roller with a conical external rollingsurface, formed in accordance with the invention, showing text gaugesfor the roller in diametral section;

FIGS. 6 and 7 are views, analogous to FIGS. 3 and 4 respectively, of themachine for forming the roller of FIG. 5.

The half-roller 1 shown in FIG. 1 is intended for use in a universaltransmission coupling, forming with an identical half-roller a rollerwhich automatically takes up play. The part-spherical surface 2 of theroller, having a radius R, rolls on ways of part-circular section, asdescribed in French Patent Application No. 7 043,789 filed by theapplicants on Dec. 4, 1970 and its associated certificate of additionNo. 7200.035 of Jan. 3, 1972.

The bore 3 of such a half-roller pivots on one axis of the transmissioncoupling while the plane face 4 bears against a special washer (notshown) disposed between the half-rollers l, as described in theabove-mentioned patent application and its certificate of addition.

Proper operation of a coupling including this type of roller calls forthe following criteria for the halfrollers:

a. the bore 3 must have a precise diameter and a very smooth surface;

b. the part-spherical zone 2 must have a good surface finish and beprecisely centred on the bore 3, its radius of curvature R must have anexactly determined value and its centre must occupy a precise positionin relation to the face 4;

c. the face 4 must be flat and exactly perpendicular to the bore 3 andmust be precisely situated with respect to the centre of curvature ofthe partspherical zone 2.

These requirements can be satisfied by means of the method andcold-forming machine in accordance with the invention.

The machine (FIG. 3) includes a die 6 with an axial bore 7 whosediameter is substantially equal to the external diameter of face 5 ofthe half-roller 1 and which flares in its upper portion to form a cup 8with a partspherical surface conforming exactly to the partsphericalsurface of the half-roller l. The cup 8 is extended as far as the upperface 9 of the die 6 by a flare 10 which is slightly conical, with ahalf-angle at the summit of the order of 5 for example.

A plunger 1 l co-operates with the die 6 and has a flat lower face 12with a central circular projection 13 having a flat lower face 14 thediameter of which is substantially equal or very slightly less than themaximum diameter of the half-roller l. The plunger 11 has an axial bore15 the diameter of which is slightly greater than that of the bore 3 inthe half-roller 1.

The die 6 rests on the't'able -16 of a press which has an aperture 17through which can passa tubular ejector 18 the outside diameter'of whichis substantially equal to the diameter of the axial bore 7 of the die 6while the inside diameter is slightly greater than that of the bore 3 inthe half-roller l.

The ejector 18has a collar 19 (FIG. 4) at its lower end which bears on ahelical spring 20 resting'on the base 21 of a cylindrical housing 22mounted beneath the press table by means of bolt 23 by means of whichthe die 6 is locked on the table 16.

Vertically reciprocable inside the ejector 18 is a burnisher 24comprising a cylindrical mandrel slightly tapered at its upper end 25and having a series of annular projections 26 forming burnishing rings.

, The plunger 11 is mounted at the end of the press piston 27.

Themechanism and controls of the press and the burnisher 24 have notbeen shown. They will be well known to those skilled in the art and formno part of the present invention.

The machine operates as follows:

The blank used is shown in FIG. 2. It consists of a ring 28 of hardtempered steel, formed on an automatic lathe. The only high precisionrequirement in respect of the machining of this ring concerns theconcentricity of its bore 29 in relation to its external cylindricalsurface 30. Said concentricity must be as perfect as commerciallypossible, since otherwise the final product has a tendency to beirregular in shape and dimensions. The ring includes chamfers 31, 32, 33and 24 which can be machined or cold-formed. The chamfers are providedso that the finished article has no sharp edges.

The press piston 27 and the plunger 11 are displaced from the die 6 andthe ejector 18 and burnisher 24 are initially in the positions shown inFIG. 3. The lubricated blank 28 is placed in the conical flare of thedie cup 8. The lubrication may be done conventionally, as withgraphitised grease for example. The blank rests on the upper end of theejector l8, and the press actuated so that the plunger 16 exerts aforming thrust on the blank to force it into the part-spherical cup 8.In this first stage the blank is axially retained on its lower face bythe ejector 18 which exerts on it a force F which increases as theejector is pushed back. This force is provided by the spring 20, but anysuitable elastic, mechanical, hydraulic or pneumatic system could beused instead of a spring. The walls of the bore 29 in the blank arepressed against the cylindrical surface of the burnisher 24.

The piston 27 descends until the lower face 12 of the plunger 11 abutsthe upper face 9 of the die 6 (FIG. 4), this abutment ensuring precisefinal relative positions of the lower face 14 of the central projection13 of the plunger and the part-spherical surface of the cup 8. Thethrust F exerted by the ejector 18 is regulated so that the pressure onthe part-spherical surface 8 developed by hydrostatic reaction issufficient to provide correct forming and polishing of the partsphericalsurface 2 of the half-roller. It should be noted that the position ofthe lower face 5 of the roller can vary as a function of the blanksvolume and without disadvantage since this face has no operativefunction.

When the external surface of the half-roller has been formed in thismanner, the burnisher 24 is raised to the position 24a shown in dashedoutline in FIG. 4 and then returned to its former position. In this waythe bore 3 of the roller is precisely dimensioned and polished.

The press piston 27 is then raised to raise the plunger 11 and theejector 18 moves upwardly under the action of the spring 20 to eject thefinished product.

As has been mentioned, the invention is also applicable to formingrollers or other bodies of revolution, without these necessarily havinga part-spherical outer surface. The invention is applicable, forexample. to forming conical rollers such as are used in roller bear- InS.

FIG. 5 shows such a roller 35 having a conical surface of revolution 36with its apex at 0 and a conical or substantially conical surface 37with apex at 0'. The angle of intersection a of the generatrices of thetwo surfaces is about 90. The cone angle of the surface 35 is 13.

The precision requirements for such a roller are concerned with:

a. the cone angles of the conical surfaces;

b. the exact coincidence of the two cone axis;

c. the exactitude of the spacing h between test calibration elements 38and 39 in the form of rings, edges 40 and 41 of which respectivelyengage the conical surfaces 36 and 37 of the roller 30.

The surface finish for each cone must be very good.

In use of the roller 30 the cone 36 carries the load on the bearingwhile the conical region 37 provides axial location of the rollers bycontact a check or edge on one of the bearing rings. The generatrices ofthis region are short. The central region 42 has no function and neednot be precisely formed. Likewise the lower face 43 of the roller neednot be precisely located, formed or finished. It should be noted thatthe roller surface 37 need not be conical. It could instead be slightlyspherical for example.

A machine for making such a roller in accordance with the invention isshown in FIG. 6. It includes a die 44 with an axial bore 45 which isupwardly flared to form a cup 46 with a conical surface whose cone angleis identical to that of the roller surface 36, 13 in this example. Theconical cup 46 leads into a passage 47 which opens onto the upper faceof the die 44 and which forms a flat bearing face 48.

A plunger 49 co-operates with the die 44 and has cylindrical outersurface 50 whose diameter corresponds to that of the die bore 47. On aflat lower face 51 of the plunger 49 is a central and circularprojection 52 whose diameter is substantially equal to the diameter ofthe largest base of the roller to be formed. The lower face 53 of theprojection 52 is conical or substantially conical and has a profileidentical to that of the roller surface 37.

The plunger 49 includes a conduit 54 which opens onto the summit of thecone formed by face 53 of the projection 52 and the upper portion of theouter wall 50 of the plunger. This conduit serves for removal of thelubricant with which the blank is coated at the beginning of the formingoperation.

The die 44 rests on a press table 55 which has a central opening 56through which passes an ejector 57 comprising a cylindrical mandrelhaving substantially the same diameter as the bore 45 of the die 44.

At its lower end the ejector has a threaded portion 58 onto which isscrewed a plate 59 which bears on a spring 60 resting on the base 61 ofa housing 62 fastened beneath the press table 55 by means of bolts 63which also serve to lock the die 44 on the table 55.

On its upper face the plunger 49 has a threaded nipple 64 screwed into athreaded axial bore 65 in the press piston 66.

The roller shown in FIG. 5 is made with this machine in the followingmanner:

The cylindrical blank 67 (FIG. 6) in hard tempered steel has plane andsubstantially parallel end faces whose diameter is substantially equalto that of the largest base of the roller to be formed. The edges oftheblank are chamfered at 68 and 69 so that after the forming operationthe roller has no sharp edges.

It is most important that said blank has a perfectly constant diameteralong its whole length, in order to obtain a final product havingprecise dimensions and a shape which corresponds exactly to what isdesired. For this purpose, blanks 67 are obtained by cutting section ofgiven length in a cylindrical metal bar which has been previously milledat the required diameter along its whole length.

The appropriately lubricated blank is placed in the conical cup 46 ofthe die 44 so as to rest on the end of the ejector 37 which is initiallyin the position shown in FIG. 6.

The press piston 66 is then lowered so that the projection 52 on theplunger 49 axially compressed the blank 67 in the conical die cup 46,overcoming the re sistance F of the spring 60 acting on the ejector 57(FIG. 7). As it descends the plunger 49 is exactly centred in relationto the die 44 due to its penetration into the bore 47 in the latter,and, at the end of its strokes, the lower face 51 of the plunger 49 isstopped at a precise position by its abutment with the bearing face 48of the die. This ensures a precise and constant dimension 11 between theconical surfaces 36 and 37 of the roller, the precision of their coneangles and surface finish being ensured by the surfaces 46 and 53 of thedie 44 and a plunger 49 respectively. Exact coincidence of the coneangles is assured by the centring of the plunger 49 in the bore 47.

As hereinabove mentioned the precision of the dimensions of the finalproduct depends from the constancy of the diameter of the initial blank.If this necessity is correctly taken into account, a remarkably preciseproduct can be obtained, and this by mere milling of the initial barfrom which the blanks are cut, whereas experience has shown that, in thepreviously known processes for cold forming of rollers of the consideredtype it was not possible to obtain precise shapes, and that anindividual milling of each roller had to be performed, such a milling ofrelatively small, frustoconical parts being of course, as a whole, muchlarger, more complicated and more expensive than the milling of a simplecylindrical bar from which a considerable num ber of blanks may be cut.

Once the roller of FIG. 1 or FIG. 5 has been formed it is hardened byquenching and suitably polished, in a drum for example.

It will be appreciated that the invention is not limited to the twojust-given examples, and that the invention is applicable to thecold-forming of various other forms of article.

We claim:

1. Apparatus for carrying out a method for coldforming a rolling elementcomprising a body of revolution with an external rolling surface havingstraight or curved generatrices extending between a portion ofrelatively large diameter, and a portion of relatively small diameter,in which method a cylindrical blank, the diameter of which issubstantially equal to the maximum diameter of the element, iscompressed in a cup whose internal profile is identical to the externalprofile of the element by overcoming an increasing counter-pressureexerted on the blank; the forcing of the blank into the cup being haltedat a predetermined stage, said apparatus comprising a die formed with acup having an internal wall the profile of which is identical to theexternal profile of said rolling surface of said element, a planebearing face of said die perpendicular to the revolution axis of saidcup, a conical extension of said wall in communication with said planebearing face of the die, a passage in said die extending from said cupsurface remote from said plane bearing face and having a diametersubstantially equal to the smallest diameter of said element, a slidingejector disposed in said bore, counter-pressure means arranged toprovide a force resisting movement of said ejector into said passage andwhich increases with the degree of penetration, a plunger having a firstbearing face adapted to engage said bearing face of the die and acircular second bearing face projecting from said first bearing face,said second bearing face having the same form as the greatest diameterface of said element and being of a size to enter said conical extensionof said cup wall, said die and said plunger being mounted for relativedisplacement so that said second bearing face of said plunger enterssaid cup, while being maintained strictly coaxial with said cup, untilsaid first bearing face of said plunger engages said bearing face ofsaid die.

2. Apparatus according to claim 1 in which said ejector is hollow andincluding a mandrel external burnishing elements on said mandrel whichproject into the said cup through said hollow ejector which is mountedfor coaxial movement within said ejector, said mandrel and saidburnishing elements having a diameter identi' cal to that of said borein said element.

3. Apparatus according to claim 1 in which the wall of said die cup ispart-spherical or toroidal.

4. Apparatus according to claim 1 in which said die cup has the form ofa cone of revolution.

5. Apparatus according to claim 1 including a press on a table of whichsaid die is located and to a piston of which said plunger is connected.

6. Apparatus according to claim 1 wherein said counter-pressure meansare resilient means.

1. Apparatus for carrying out a method for cold-forming a rollingelement comprising a body of revolution with an external rolling surfacehaving straight or curved generatrices extending between a portion ofrelatively large diameter, and a portion of relatively small diameter,in which method a cylindrical blank, the diameter of which issubstantially equal to the maximum diameter of the element, iscompressed in a cup whose internal profile is identical to the externalprofile of the element by overcoming an increasing counter-pressureexerted on the blank; the forcing of the blank into the cup being haltedat a predetermined stage, said apparatus comprising a die formed with acup having an internal wall the profile of which is identical to theexternal profile of said rolling surface of said element, a planebearing face of said die perpendicular to the revolution axis of saidcup, a conical extension of said wall in communication with said planebearing face of the die, a passage in said die extending from said cupsurface remote from said plane bearing face and having a diametersubstantially equal to the smallest diameter of said element, a slidingejector disposed in said bore, counter-pressure means arranged toprovide a force resisting movement of said ejector into said passage andwhich increases with the degree of penetration, a plunger having a firstbearing face adapted to engage said bearing face of the die and acircular second bearing face projecting from said first bearing face,said second bearing face having the same form as the greatest diameterface of said element and being of a size to enter said conical extensionof said cup wall, said die and said plunger being mounted for relativedisplacement so that said second bearing face of said plunger enterssaid cup, while being maintained strictly coaxial with said cup, untilsaid first bearing face of said plunger engages said bearing face ofsaid die.
 2. Apparatus according to claim 1 in which said ejector ishollow and including a mandrel external burnishing elemenTs on saidmandrel which project into the said cup through said hollow ejectorwhich is mounted for coaxial movement within said ejector, said mandreland said burnishing elements having a diameter identical to that of saidbore in said element.
 3. Apparatus according to claim 1 in which thewall of said die cup is part-spherical or toroidal.
 4. Apparatusaccording to claim 1 in which said die cup has the form of a cone ofrevolution.
 5. Apparatus according to claim 1 including a press on atable of which said die is located and to a piston of which said plungeris connected.
 6. Apparatus according to claim 1 wherein saidcounter-pressure means are resilient means.